Diophantus' riddle

One of the oldest known age puzzles.
It comes from the Greek Anthology, a collection of puzzles compiled
by Metrodorus in about AD
500, and purports to tell how long Diophantus
lived in the form of a riddle engraved on his tombstone:

God vouchsafed that he should be a boy for the
sixth part of his life; when a twelfth was added, his cheeks acquired
a beard; He kindled for him the light of marriage after a seventh, and
in the fifth year after his marriage He granted him a son. Alas! late-begotten
and miserable child, when he had reached the measure of half his father's
life, the chill grave took him. After consoling his grief by this science
of numbers for four years, he reached the end of his life.

If d and s are the ages of Diophantus and his son when
they died, then the epitaph boils down to these two equations:

d = (1/6 + 1/12 + 1/7)d
+ 5 + s + 4s = 1/2
d

which can be solved simultaneously to give s = 42 years and d
= 84 years.